Economizer/dcv controller with manual sensor calibration

ABSTRACT

An economizer controller with sensor calibration. A controller sensor may be used to measure a parameter. At the same time at the same location of the measurement with the controller sensor, a measurement of the same parameter may be made with a precision sensor. The difference between the two measurements may be saved to a controller memory as an offset. The offset may be used to compensate future measurements of the same parameter by the controller sensor. Additional offsets at various magnitudes may be obtained between the precision and the controller sensors for compensating subsequent measurements by the controller sensor. Measurements with the compensated sensor may be used for calibrating sensors in other economizer controllers, for example, at remote locations in the field.

This application is a continuation of U.S. patent application Ser. No. 12/890,380, filed Sep. 24, 2010. U.S. patent application Ser. No. 12/890,380, filed Sep. 24, 2010, is hereby incorporated by reference.

BACKGROUND

The present disclosure pertains to controllers and particularly to economizer controllers. More particularly, this disclosure pertains to compensation of sensors for economizer controllers.

SUMMARY

The disclosure reveals an economizer controller with sensor calibration. A controller sensor may be used to measure a parameter. At the same time, at the same location of the measurement with the controller sensor, a measurement of the same parameter may be made with a precision sensor. The difference between the two measurements may be saved to a controller memory as an offset. The offset may be used to compensate future measurements of the same parameter by the controller sensor. Additional offsets at various magnitudes may be obtained between the precision and the controller sensors for compensating subsequent measurements by the controller sensor. Measurements with the compensated sensor may be used for calibrating sensors in other economizer controllers, for example, at remote locations in the field.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram of obtaining a setting from a precision sensor;

FIG. 2 is a diagram of compensating the system sensor; and

FIG. 3 is a schematic of a representative economizer system.

DESCRIPTION

Energy savings and precise environmental control are continually gaining importance as energy costs rise. In the effort to better control, and optimize energy use for environmental controls, the accuracy of the individual sensing elements in the system become more and more important. This drives an ever increasing commercial need for accurate sensing solutions.

This disclosure may solve the need by allowing precision sensors to be calibrated for accuracy when coupled with an economizer controller. This may be a digital economizer/DCV (demand controlled ventilation) controller that has a capability for manually calibrating individual sensors in the field.

The invention may be implemented in economizer firmware. When a customer would like to calibrate an individual sensor in an economizer/DCV system, the controller may be placed in calibration mode. Then the customer is able to calibrate each sensor to a reference. This calibration offset may then be stored in the firmware and used to compensate sensor data before submitted to the next level of firmware.

FIG. 1 is a diagram of obtaining a setting from a precision sensor. A calibration start 11 may begin by going to read a system sensor at symbol 12. A precision sensor may be brought in and a value of the precision sensor may be obtained at symbol 13. With the value of the precision sensor, the system sensor offset may be computed at symbol 14. With the sensor offset at symbol 15, then one may be at a calibration end 16.

FIG. 2 is a diagram of compensating the system sensor. A sensor compensation start 18 may begin by reading the system sensor at symbol 19. With the sensor offset at symbol 15, a compensated value of the system sensor may be computed at symbol 21. Then one may be at a sensor compensation end 22.

FIG. 3 is a schematic of a representative economizer system 50. A thermostat 51 may be connected to an economizer logic module 52. A demand control ventilation sensor 53 may be connected to module 52. Return air 54 may come in through a recirculation damper 55 into a mixing air chamber 56 where air 54 may be mixed with outdoor air 57 coming through an intake damper 58. Mixed air may be discharge air 59 which is drawn by an indoor fan 61 through a direct expansion coil 62 and provided to a space being conditioned via a supply duct 68. Dampers 55 and 58 may be controlled by an actuator 63 which is connected to module 52. Damper 58 may close as damper 55 opens and vice versa. A portion of return air 54 may taken from return air duct 64 and drawn through a damper 65 by an exhaust fan 66 through an exhaust duct 76 to outside the system as exhaust air 67. Exhaust fan 66 may be connected to module 52. The position of damper 65 may be determined at least in part by module 52. The proportions of outdoor air 57 and recirculated air 54 taken into supply duct 68, as well as the amount of air 67 from return air duct 64, may be controlled by intake damper 58, recirculation damper 55 and exhaust damper 65. An enthalpy sensor 71 situated in an intake or outdoor air duct 73 may be connected to module 52. For differential enthalpy, a second enthalpy sensor 72, along with enthalpy sensor 71, may be connected to module 52.

A mixed air sensor 74 may be situated in chamber or duct 56, or a discharge air sensor 75 may situated in chamber or duct 68, but not necessarily both. One or the other of or both sensors 74 and 75 may be connected to logic module 52. There may be situations where there would be both a mixed air sensor in the mixed air chamber and a separate discharge air sensor in the discharge chamber or duct. There may also be situations where there is not a discharge air sensor but that a mixed air sensor is mounted in the discharge chamber or duct.

Economizers may save energy in buildings by using cool outside air as a means of cooling the indoor space. When the enthalpy of the outside air is less than the enthalpy of the recirculated air, conditioning the outside air may be more energy efficient than conditioning recirculated air. When the outside air is both sufficiently cool and sufficiently dry (depending on the climate), the amount of enthalpy in the air is acceptable to the control, no additional conditioning of it is necessarily needed. This portion of the air-side economizer control scheme may be referred to as free cooling.

Economizers may reduce HVAC energy costs in cold and temperate climates while also potentially improving indoor air quality, but they might often not be appropriate in hot and humid climates. With the proper controls, economizers may be used in climates which experience various weather systems.

When the outside air's dry-bulb and wet-bulb temperatures are low enough, economizers may use water cooled by a wet cooling tower to cool buildings without operating a chiller. Often a plate-and-frame heat exchanger may be inserted between the cooling tower and chilled water loops.

To recap, the present calibrating mechanism for an economizer controller may have a precision sensor of a first kind and a first system sensor of the first kind of an economizer controller. The first system sensor may be read to obtain a first value in a first ambient environment at a first time. The precision sensor may be read to obtain a second value in the first ambient environment at the first time. The first value may be compared with the second value to obtain a first offset from a difference between the first and second values. The first system sensor may be read to obtain a third value at a second time. The third value of the first system sensor may be adjusted by incorporating the first offset to obtain a compensated third value of the first system sensor.

The calibrating mechanism may further have a second system sensor of the first kind of a second economizer controller. The second system sensor may be read to obtain a fourth value in a second ambient environment at a third time. The first system sensor may be read to obtain a fifth value in the second ambient environment at the third time. The fifth value of the first system sensor may be adjusted by incorporating the first offset to obtain a compensated fifth value of the first system sensor. The fourth value may be compared with the compensated fifth value to obtain a second offset from a difference between the fourth and compensated fifth values. The second system sensor may be read to obtain a sixth value at a fourth time. The sixth value of the second system sensor may be adjusted by incorporating the second offset to obtain a compensated sixth value of the second system sensor.

The first system sensor may be read to obtain a fourth value in the first ambient environment at a third time. The precision sensor may be read to obtain a fifth value in the first ambient environment at the third time. The fourth value of the first system sensor may be compared with the fifth value of the precision sensor to obtain a second offset from a difference between the fourth and fifth values.

The first and second offsets may be combined to provide a curve of offsets versus values from the first system sensor, which can be extrapolated for obtaining offsets for other values obtained by the first system sensor. The curve may be extrapolated for obtaining offsets for compensating various values from the first system sensor. The first system sensor may be read to obtain a sixth value at a fourth time. An offset may be determined from the curve for compensating the sixth value.

A sensor of the first kind may be a temperature sensor, a relative humidity sensor, a CO2 sensor, or the like.

The approach for calibrating a system sensor in an economizer controller may incorporate measuring a first parameter with a system sensor of an economizer controller to get a first reading, and measuring the first parameter with a precision sensor to get a second reading. It may further incorporate computing an offset from a difference between the first and second readings, entering the offset into a memory of the economizer controller, and using the offset for calibrating other readings from the system sensor.

The first reading from the system sensor may be an X. The second reading from the precision sensor may be a Y. IX-YI may be the offset. If X is greater than Y, then the offset may be subtracted from a subsequent reading from the system sensor for compensation of the subsequent reading. If Y is greater than X, then the offset may be added to a subsequent reading from the system sensor for compensation of the subsequent reading.

The readings of the precision sensor and the system sensor may be stored in the economizer controller. A determination for the offset from the readings of the precision sensor and the system sensor, and compensation of a subsequent reading of the system sensor may be automatically processed by the economizer controller.

The approach may further incorporate measuring the first parameter with the system sensor of the economizer controller to get a first reading at each of a plurality of ambient temperatures, and measuring the first parameter with the precision sensor to get a second reading at each of the plurality of ambient temperatures. Also, the approach may incorporate computing an offset from a difference between the first and second readings of the first parameter for each of the plurality of ambient temperatures, and using an offset, computed at a temperature of the plurality of ambient temperatures, for calibrating another reading from the system sensor of the first parameter obtained at the same temperature that the offset was computed. The first parameter may be a non-temperature parameter.

An approach for calibrating a system sensor of an economizer controller, may incorporate taking a plurality of readings with a system sensor of an economizer controller at a first set of different values of a parameter, and taking a plurality of readings with a precision sensor at the first set of different values of the parameter for the first set of different values. Then a plurality of offsets may be determined where each offset is a comparison of a reading from the system sensor and a reading from the precision sensor at a same time, of the parameter for the first set of different values. A reading from the system sensor of a certain value of the parameter may be compensated with an offset from the plurality of offsets for a value, of the first set of different values, most closely corresponding to the certain value.

The approach may further incorporate a graphing the plurality of offsets versus readings of the system sensor. Each offset of the plurality of offsets and each corresponding reading of the system sensor may be plotted as a point on a graph resulting in a plurality of points on the graph. A curve may be constructed that fits on the plurality of points on the graph. The plurality of offsets versus readings of the system sensor may be entered in a look-up table.

Compensating a reading from the system sensor of a certain value of the parameter with an offset from the plurality of offsets for a value corresponding to the certain value may be automatic by the economizer controller for each reading from the system sensor of the parameter.

The economizer controller may incorporate a user interface for placing the controller in a calibration mode for compensating a reading with an offset determined by a reading from each system sensor relative to a reading from the precision sensor. Offsets determined for readings of each system sensor may be stored at the controller for availability for compensating a reading from a system sensor at the controller in absence of the precision sensor.

The economizer controller may be a digital controller with demand controlled ventilation (DCV).

U.S. Pat. Nos. 6,161,764, 4,570,448, and 7,434,413 may be relevant. U.S. Pat. No. 6,161,764, issued Dec. 19, 2000, is hereby incorporated by reference. U.S. Pat. No. 4,570,448, issued Feb. 18, 1986, is hereby incorporated by reference. U.S. Pat. No. 7,434,413, issued Oct. 14, 2008, is hereby incorporated by reference.

In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.

Although the present system has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications. 

What is claimed is:
 1. A system for calibrating an economizer controller, comprising: a first system sensor configured to obtain a first value of a first control parameter of an HVAC system; a first precision sensor configured to obtain a second value of a same type as the first value related to the first control parameter, the first precision sensor configured to obtain the second value at a same time as the first system sensor obtains the first value; wherein the economizer controller is configured to compare the first value of the first system sensor is with the second value of the first precision sensor to obtain a first offset; and wherein the first offset is stored in a firmware of the economizer controller and is used to compensate the first system sensor.
 2. The system of claim 1, wherein the first system sensor is configured to obtain a third value of a the first control parameter at a second time and the first precision sensor is configured to obtain a fourth value of a same type as the third value at the second time the first system sensor obtains the third value.
 3. The system of claim 2, wherein the economizer controller is configured to compare the third value of the first system sensor is with the fourth value of the first precision sensor to obtain a second offset.
 4. The system of claim 3, wherein the first and second offsets are combined to provide a curve of offsets versus values from the first system sensor, which is extrapolated for obtaining offsets for other values obtained by the first system sensor.
 5. The system of claim 1, wherein the first system sensor is a temperature sensor.
 6. The system of claim 1, wherein the first system sensor is a relative humidity sensor.
 7. The system of claim 1, wherein the first system sensor is a CO2 sensor.
 8. A method for calibrating a system sensor in a demand control ventilation system, the method comprising: placing a demand control ventilation system controller into a calibration mode; measuring a first control parameter of the demand control ventilation system with a system sensor to obtain a first reading at a first time; measuring the first control parameter with a precision sensor to obtain a second reading at the first time and in a same ambient environment as the system sensor; computing an offset from a difference between the first and second readings; and entering the offset into a memory of an economizer controller.
 9. The method of claim 8, wherein: the absolute value of the different in the first and second reading is the offset; if the first reading is greater than the second reading, then the offset is subtracted from a subsequent reading from the system sensor for compensation of the subsequent reading; and if second reading is greater than the first reading, then the offset is added to a subsequent reading from the system sensor for compensation of the subsequent reading.
 10. The method of claim 8, wherein: the readings of the precision sensor and the system sensor are stored in the demand control ventilation system controller; and determination for the offset from the readings of the precision sensor and the system sensor, and compensation of a subsequent reading of the system sensor are automatically processed.
 11. The method of claim 8, wherein determination for the offset from the readings of the precision sensor and the system sensor, and compensation of a subsequent reading of the system sensor are automatically processed by the economizer controller.
 12. The method of claim 8, further comprising: measuring the first control parameter with the system sensor of the economizer controller to get a first reading at each of a plurality of times at a plurality of ambient temperatures; and measuring the first control parameter with the precision sensor to get a second reading at each of the plurality of times and the plurality of ambient temperatures
 13. The method of claim 12, further comprising: computing an offset from a difference between the first and second readings of the first control parameter for each of the plurality of times and plurality of ambient temperatures; and using an offset, computed at a temperature of the plurality of ambient temperatures, for calibrating another reading from the system sensor of the first control parameter obtained at the same temperature that the offset was computed.
 14. The method of claim 8, wherein the first control parameter is a temperature parameter.
 15. The method of claim 8, wherein the first control parameter is a non-temperature parameter.
 16. A method for calibrating a system sensor of an economizer controller, comprising: placing the economizer controller into a calibration mode; taking a plurality of readings with a system sensor of the economizer controller at a plurality of times to obtain a first set of different values of a parameter; taking a plurality of readings with a precision sensor at a same plurality of times as the system sensor to obtain a second set of values of the parameter; determining a plurality of offsets wherein each offset is a comparison of a reading from the system sensor and a reading from the precision sensor at a same time; and compensating a reading from the system sensor of a certain value of the parameter with an offset from the plurality of offsets for a value most closely corresponding to the certain value.
 17. The method of claim 16, further comprising: graphing the plurality of offsets versus readings of the system sensor; and constructing a curve that fits on the plurality of points on the graph.
 18. The method of claim 16, wherein the plurality of offsets versus readings of the system sensor are entered in a look-up table.
 19. The method of claim 16, wherein the compensating a reading from the system sensor of a certain value of the parameter with an offset from the plurality of offsets for a value corresponding to the certain value is automatically performed by the economizer controller for each reading from the system sensor of the parameter.
 20. The method of claim 16, wherein the economizer controller is a digital controller with demand controlled ventilation. 